What psi of oil pressure is suggested on a 350 engine at idle and cruising speed?

If everything is working properly, the oil pressure will be controlled by a "bypass" valve inside the engine. Once the oil pump builds enough pressure, any additional volume is "dumped" back into the crankcase so that the oil lines don't build up too much pressure and damage the bearings and oil pump.
When the engine is cold, you should see the MAXIMUM oil pressure. Start the engine, watch the oil pressure and see where it goes. The needle will rise rapidly until the bypass valve starts dumping excess oil. Wherever the needle stops, that's your normal oil pressure. Usually it's somewhere in the middle of the gauge, 40 to 60 psi, but the exact number isn't critical. What's important is keeping it in that range... wherever the bypass takes over. If the engine warms up and the oil pressure starts to go down, you have worn bearings. That's the most common reason for a loss of oil pressure in the 350 engine. It's a great old engine, as tough as they get. If the oil pressure is starting to go down when the engine is warm, just change to a heavier grade oil at your next oil change. If you've been using 5W15, change to 10W30 or even heavier. That will help you get a lot more life out of the engine. The thicker oil will keep the worn bearings lubricated better and help the engine last longer.